1. Field of the Invention
This invention relates to piezoelectric transducer devices in which the active element consists of a polymeric material having piezoelectric properties which are similar to those of substances belonging to certain classes of crystals when said material has been subjected to a suitable treatment. Polymers in which such effects can be developed are numerous. The following can be mentioned by way of indication: polyvinylidene fluoride (PVF.sub.2), polyvinyl chloride (PVC), polyvinyl fluoride (PVF) as well as copolymers such as, for example, polytetrafluoroethylene-polyvinylidene fluoride (PTFE-PVF.sub.2).
2. Description of the Prior Art
In the known art, these materials are employed in the form of flat films which are metallized on both faces and may or may not have been oriented mechanically but are polarized in all cases by application of an intense electric field (of the order of 1 MV/cm) at a temperature which is higher than or equal to room temperature. By means of this treatment, films of polymeric material acquire piezoelectric properties which makes it possible to employ them as transducers. Potential applications of these flat films include pressure and displacement sensors (microphones, hydrophones, strain gages, and so on). More recently, it has been proposed to employ these materials after thermoforming or molding in suitable shapes so as to produce earphone, loudspeaker or microphone diaphragms. Transducer devices of this type are described, for example, in French patent application No. 77 34 589 filed on Nov. 17, 1977 in the name of the present applicant and published under No. 2,409,654.
Fabrication of these transducers gives rise to many problems of a technological order, such as those related to coating operations, leading-out of connecting wires, the choice of design parameters which becomes more difficult as the transducer or sensor is of smaller size, and problems of metallization for the formation of electrodes. The size of a sensor is greatly dependent on the type of measurement to be performed (point measurement, measurement integrated on a surface), with the result that each sensor has to be designed as a function of the purpose for which it is specifically intended. Furthermore, certain types of measurement require a very large number of transducers.
In the case of many applications, it would be an advantage to be able to make use of inexpensive transducers fabricated from standardized elements on a large-scale, continuous production basis.
In order to satisfy these requirements, the invention proposes transducer devices having a structure which is similar to that of multiconductor electric cables and manufactured in accordance with the same techniques. Some variants also permit the direct use of electric cables of the type comprising an insulator made of polymeric material and activated by means of a treatment which is identical in all respects to the treatment employed for activating the polymer sheets of transducer materials of the prior art. The invention also proposes molded transducer devices involving the application of techniques usually employed for producing connectors.